Most of the scholars in India use red color Henna (mahandi) for their beard. I asked most of them but they said it is allowed in Islam, but some says it is Sunnah. But as for my information the tree which these leaves come, it will not growth in desert area, but all Arab is have full desert. From where these leave come to our Prophet they say it is Sunnah. As my hair and my beard became white my parents and my specially wife forcing me to apply Henna. What is your Fatwa regarding this?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

Dyeing the hair with Henna is a confirmed Sunnah of the Prophet ; he did it, said it and confirmed it. 'Uthamaan Ibn Mawhib said: "I entered to the house of Um Slamah, so she showed me some hair of the Prophet dyed with Henna and Katam (a kind of dark Henna)." [Ahmad and Ibn Maajah] Furthermore, the Prophet said: "The best thing with which you dye your grey hair is Henna and Katam." [An-Nasaa'ee]

Moreover, Ibn 'Abbaas narrated: "A man who dyed his hair with Henna passed by the Prophet . Upon seeing him, the Prophet said: "This man did really well." [Abu Daawood] Besides, Imaam Muslim reported that Abu Bakr and 'Umar dyed their hair with Henna. Therefore, there is no way in doubting over the permissibility of dyeing the hair with Henna or doubting whether or not this is a Sunnah. The fact that Henna does not grow in the desert and believing that the Prophet was unlikely to obtain it, does not affect the religious ruling. Even if we suppose that Henna does not grow in the desert, it is still possible to obtain it through the caravans which travel to Ancient Syria and other countries. It is well-known that the Arabs in general and the tribe of Quraysh in particular used to travel to Ancient Syria  and Yemen in winter and summer times.

In short, the Prophet obtained and used Henna whether it grew in the desert or obtained it through the tradesmen.

Finally, we advise you to obey your parents if they order you to dye your hair as it is an obligation to obey the parents within what is permissible.  

Allaah Knows best.